1. Field of the Invention
The present invention relates generally to a radio frequency plasma source and, more particularly, to a plasma processing system using a radio frequency plasma source.
2. Discussion of the Related Art
Plasma is a highly ionized gas which contains equal numbers of positive ions and electrons. Plasma discharge is used for gas excitation of active gas containing ions, free radicals, atoms and molecules. The active gas is generally used in various fields, and typically, during the semiconductor fabrication processes, such as etching, deposition, cleaning and ashing.
There are various plasma sources for generating plasma, and typical examples are a capacitively coupled plasma source and an inductively coupled plasma source, and both sources use a radio frequency.
The capacitively coupled plasma source accurately controls the capacity and ion, and has high processing productivity in comparison to other plasma sources. Since the energy of the radio frequency power is almost exclusively connected to plasma by capacitive coupling, the plasma ion density increases or decreases based solely upon the increase or decrease of the capacitively-coupled radio frequency power. Any increase in the radio frequency power, however, increases ion impact energy. Consequently, the radio frequency power must be limited to prevent damage caused by ion impact.
The inductive coupled plasma source readily increases the ion density as the radio frequency power increases. In the inductive coupled plasma source, the ion impact caused by an increase in the radio frequency power will be relatively low. Thus, the inductive coupled plasma source is suitable to generate high-density plasma. One technique for inductive coupled plasma source has used a RF antenna and a transformer, and is generally referred to as transformer coupled plasma. In an effort to improve the characteristics of the plasma and to enhance the reproductability and control performance of this technique, the method of using an RF antenna or a transformer has further endeavored to additionally use either an electromagnet or a permanent magnet, or a capacitive coupled electrode.
Generally, either a spiral type antenna or a cylinder type antenna is used as an RF antenna. The RF antenna is positioned outside a plasma reactor, and transfers an inductive electromotive force into the plasma reactor through a dielectric window such as quartz. The inductively coupled plasma source using an RF antenna easily generates high-density plasma. The structural feature of the antenna however, affects the plasma uniformity in the inductive coupled plasma source. Thus, further research efforts have been conducted to an attempt improve the structure of an RF antenna so as to produce uniformly high-density plasma.
There is a limit to the enlargement of the structure of the antenna and to an increase in the power supplied to the antenna in an attempt to obtain large-area plasma. For example, it is known that non-uniform plasma is radially generated by a standing wave effect. Furthermore, when high power is applied to the antenna, the thickness of the dielectric window should be thick because the capacitive coupling of the RF antenna increases. Thus, since the distance between the RF antenna and plasma is increased, the power transfer efficiency is reduced.
In an inductive coupled plasma source using a transformer, i.e., a transformer coupled plasma source, plasma is induced in a plasma reactor by using the transformer, and the inductive coupled plasma completes a second circuit of the transformer. Techniques for transformer coupled plasma sources have been developed by either including an outer discharge tube in a plasma reactor, mounting a closed core in a toroidal chamber, or including a transformer core inside the plasma reactor.
One transformer coupled plasma source has been developed to improve characteristics of plasma and the energy transfer characteristics thereof by improving the plasma reactor structure and using a transformer coupling structure. Specifically, in order to obtain large-area plasma, the coupling structure of the transformer and the plasma reactor is improved, a number of outer discharge tubes are included, or alternatively, the number of transformer cores mounted inside the plasma reactor is increased. It is not easy however, to uniformly produce large-area high-density plasma by merely increasing the number of outer discharge tubes or the number of transformer cores.
As semiconductor devices becomes super-miniaturized, silicon wafer substrates for fabricating a semiconductor circuits become larger, the glass substrate for manufacturing liquid crystal displays becomes bigger, and as new materials to be processed appear, plasma processing techniques must be improved in order to update semiconductor fabrication industry. Specifically, a plasma source and a plasma processing technique must have excellent processing performance to enable large-area workpieces to be processed.
Furthermore, as the substrate to be processed becomes larger, the whole of the manufacturing equipment also becomes larger, thereby increasing the required equipment area and, concomitantly increasing manufacturing costs. Thus, if possible, a plasma source and a plasma processing system must minimize the equipment area.